Tapered block copolymers of monovinylarenes and conjugated dienes

ABSTRACT

A method for preparing tapered block copolymers which are particularly useful for blend components in blends with polymers of styrene. In the first embodiment of this invention the copolymers are prepared in a polymerization process by sequentially charging: (1) an initiator and monovinylaromatic monomers in the presence of a randomizer; (2) an initiator and monovinylaromatic monomers; (3) a mixture of monovinylaromatic and conjugated diene monomers; and (4) a coupling agent; to produce a polymodal tapered block copolymer. In a second embodiment of the invention tapered block copolymers are prepared in a polymerization process by sequentially charging: (1) an initiator and monovinylaromatic monomers in the presence of a randomizer; (2) an initiator and monovinylaromatic monomers; (3) a mixture of monovinylaromatic and conjugated diene monomers; (4) a mixture of monovinylaromatic and conjugated diene monomers; and (5) a coupling agent; to produce a polymodal tapered block copolymer. The invention copolymers and blends of the invention copolymers with polymers of styrene are particularly useful for applications such as packaging and food or drink containers which require transparency, low blueness, colorlessness, good impact strength and ductility.

This application is a File Wrapper Continuation of application Ser. No.08/651,135, filed May 21, 1996, now abandoned, which is a divisional ofapplication Ser. No. 08/478,306, filed Jun. 7, 1995, now U.S. Pat. No.5,545,690, which is a divisional of application Ser. No. 08/153,408,filed Nov. 15, 1993, now abandoned.

FIELD OF THE INVENTION

This invention relates to tapered block copolymers of monovinylarenesand conjugated dienes and methods of preparation of these tapered blockcopolymers.

BACKGROUND OF THE INVENTION

There has developed in the polymer field, and especially in thepackaging and related industries, a need for thermoplastic polymers thatcan be formed into colorless, transparent articles having good impactstrength and ductility. There are needs for polymers which are useful assingle components as well as for use in blends with other commonly usedpolymers to make articles with improved properties. The polymerssatisfying these needs should be suitable for use with conventionalextrusion, injection and blow molding equipment and also suitable foruse in other methods of forming plastics into containers, tubes, films,fibers, and the like. Polystyrene, high impact polystyrene, branchedblock copolymers, and the like have been developed to meet thesecriteria with various degrees of satisfaction.

Much effort has been directed to the preparation of substantiallytransparent block copolymer resins with a variety of block structuresproduced by a variety of monomer addition sequences and a variety ofcoupling agents. Desirable properties and an economic advantage can beobtained by blending some monovinylaromatic-conjugated diene copolymerswith polystryene polymers. However, because blueness of blends ofmonovinylaromatic-conjugated diene copolymers with polystyrene polymerscannot be predicted by rule of mixtures behaviors, getting a desirablecombination of properties can be a complicated task. Sometimesrelatively colorless monovinylaromatic-conjugated diene copolymers giveblends with high blueness when blended with colorless general purposepolystyrene.

Blueness of articles formed from various copolymers and blends ofcopolymers with other polymers is a longstanding problem in applicationswhere colorless materials which also have good impact strength andductility are desirable. Specific examples include materials for waterand food containers.

SUMMARY OF THE INVENTION

It is an object of this invention to provide novel resinous taperedblock copolymers of vinyl-substituted aromatic hydrocarbons andconjugated dienes from which can be made articles with low blueness andacceptable impact strength and ductility.

It is another object of this invention to provide novel resinous taperedblock copolymers of vinyl-substituted aromatic hydrocarbons andconjugated dienes suitable for use in blends with polymers of styrene,particularly blends from which can be made articles that exhibit lowblueness and acceptable impact strength and/or ductility. Further, it isan object to provide novel resinous tapered block copolymers ofvinyl-substituted aromatic hydrocarbons and conjugated dienes which canbe used in smaller amounts than some of the other commonly used resinouspolymodal monovinyl substituted aromatic-conjugated diene blockcopolymers in blends with polymers of styrene to achieve similarly lowblueness levels and good impact strength and/or ductility in articlesmade from the blends.

A further object of this invention is to provide novel processes formaking resinous tapered block monovinylaromatic/conjugated dienescopolymers, including copolymers suitable for use in blends.

In a first embodiment of the invention, copolymers are prepared undersolution polymerization conditions in a reaction zone by:

(a) charging a monovinylaromatic monomer and an initiator in thepresence of a randomizer and allowing polymerization to occur untilessentially no free monomer is present; thereafter

(b) charging an initiator and a monovinylaromatic monomer and allowingpolymerization to occur until essentially no free monomer is present;thereafter

(c) charging a mixture of monovinylaromatic monomer and conjugated dienemonomer and allowing polymerization to occur until essentially no freemonomer is present; and thereafter

(d) charging the reaction mixture wit h a coupling agent.

In a second embodiment of the invention, copolymers are prepared in thesame manner as those of the first embodiment, except that additionally,after step (c) and preceeding step (d), a second separate charge of amixture of monovinylaromatic monomer and conjugated diene monomer ismade a n d allowed to polymerize until essentially no free monomer ispresent before charging the reaction mixture with a coupling agent.

DETAILED DESCRIPTION OF THE INVENTION

We have discovered novel monovinylaromatic/conjugated diene taperedblock copolymers which can be used neat or blended with polymers ofstyrene to produce resins which can be formed into articles with lowblueness and advantageous impact properties and/or ductility.

The polymers of this invention are characterized as resinous non-rubberyblock copolymers of at least one conjugated diene with at least onemonovinylarene, having at least one random-tapered block and areprepared so that, when the choice of coupling agent permits, at least aportion of the final product is of a branched, coupled character.

The polymers prepared according to this invention contain from about 55to about 95, preferably from about 60 to about 90, more preferably fromabout 65 to about 85, weight percent of copolymerized monovinyl aromaticmonomer based on the weight of total monomers employed. Correspondingly,the inventive copolymers contain from about 45 to about 5, preferablyfrom about 40 to about 10, and more preferably from about 35 to about 15weight percent copolymerized conjugated diene monomer based on the totalweight of monomers in the copolymer.

The coupled portions of the resinous polymodal block copolymers of thisinvention have terminal polymonovinylarene blocks on the extending armsof each linear or radial copolymer molecule, and further contain atleast one internal tapered block of monovinylarene and conjugated diene.The resinous copolymeric polymodal products also contain portions oflinear uncoupled block copolymers ofpoly(monovinylarene)-poly(conjugated diene); the linear uncoupled blockcopolymer content is considered to be an important portion of theresinous product with respect to its overall properties.

Components

The process of this invention can be carried out using as an initiatorany of the organomonoalkali metal compounds of the formula RM wherein Ris an alkyl, cycloalkyl or arylcarbanion containing 4 to 8 carbon atomsand H is an alkyl metal cation. Mixtures of organoalkali metal compoundscan be used. The presently preferred initiators are alkylmonolithiumcompounds, especially n-butyllithium or sec-butyllithium.

The conjugated diene monomers which can be used contain 4 to 6 carbonatoms and include 1,3-butadiene, 2-methyl-1,3-butadiene,2-ethyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene andmixtures thereof. Each of the charges containing conjugated diene in thesame sequence of charges may be the same, but is not necessarily thesame, conjugated diene monomer or mixture of conjugated diene monomers.The presently preferred conjugated diene monomer is 1,3-butadiene.

The monovinylaromatic monomers which can be used contain 8 to 12 carbonatoms and include styrene, alpha-methylstyrene, 4-methylstyrene,3-methylstyrene, 2-methylstyrene, 4-ethylstyrene, 3-ethylstyrene,2-ethylstyrene, 4-tert-butylstyrene, 2,4-dimethylstyrene and condensedaromatics such as vinyl napthalene and mixtures thereof. Each of thecharges containing monovinylaromatic monomer in the same sequence ofcharges may be the same, but is not necessarily the same,monovinylaromatic monomer or mixture of monovinylaromatic monomers. Thepresently preferred monovinylaromatic monomer is styrene.

Examples of polar compounds which can be advantageously employed asrandomizers are ethers, thioethers (sulfides) and tertiary amines. It isusually preferred to use ethers and sulfides in which the radicalsattached to the oxygen or sulfur atoms are hydrocarbon radicals.Specific examples of such polar materials include dimethyl ether,diethyl ether, ethyl methyl ether, ethyl propyl ether, di-n-propylether, di-n-octyl ether, anisole, dioxane, 1,2-dimetboxyethane, dibenzylether, diphenyl ether, 1,2-dimethoxybenzene, tetramethylene oxide(tetrahydrofuran), dimethyl sulfide, diethyl sulfide, di-n-propylsulfide, di-n-butyl sulfide, methyl ethyl sulfide, dimethylethylamine,tri-n-ethylamine, tri-n-propylamine, tri-n-butylamine, trimethylanine,triethylamine, tetramethylethylenediamine, tetraethylethylenediamine,N,N-di-methylaniline, N-methyl-N-ethylaniline, N-methylmorpholine, andthe like. It is to be understood also that mixtures of these polarcompounds can be employed in the practice of the present invention. Thepolar compounds are generally used in admixture with the hydrocarbondiluent. Presently preferred are either tetrahydrofuran or diethylether.

Among the suitable coupling agents are the di- or multivinylaromaticcompounds, di- or multiepoxides, di- or multiisocyanates, di- ormultiimines, di- or multialdehydes, di- or multiketones, alkoxytincompounds, di- or multihalides, particularly silicon halides andhalosilanes, mono-, di-, or multianhydrides, mono-, di-, or multiesters,preferably the esters of monoalcohols with polycarboxylic acids,diesters which are esters of monohydric alcohols; with dicarboxylicacids, lactones, and the like, including compounds containing two ormore groups and mixtures of two or more compounds.

Examples of suitable vinylaromatic coupling agents include, but are notlimited to, divinylbenzene, 1,2,4-trivinylbenzene,1,3-divinylnaphthalene, 1,3,5-trivinylnaphthalene, 2,4-divinylbiphenyl,p-diisopropenylbenzene, and the like. Of these, the divinylaromatichydrocarbons are preferred, particularly divinylbenzene in either itsortho, meta, or para isomer. Commercial divinylbenzene which is amixture of the three isomers and other compounds is satisfactory.

Epoxidized hydrocarbon polymers such as epoxidized liquid polybutadieneand epoxy compounds such as 1,2; 5,6; 9,10-triepoxydecane, and the like,can be used as coupling agents.

Organoalkyl phosphites and arylalkyl phosphites are considered useful ascoupling agents in this invention.

Examples of suitable multilsocyanate coupling agents includebenzene-1,2,4-triisocyanate, naphthalene-1,2,5,7-tetraisocyanate, andthe like. Commercially available products known as PAPI-1, apolyarylpolyisocyanate having an average of 3 isocyanate groups permolecule and an average molecular weight of about 380 are suitable.

The multiimines, also known as multiaziridinyl compounds, such as thosecontaining 3 or more aziridine rings per molecule, are useful ascoupling agents. Other compounds useful as coupling agents includetetravinyl silane, trivinyl phosphine, the triaziridinyl phosphineoxides or sulfides such as tri(1-aziridinyl)phosphine oxide,tri(2-methyl-1-aziridinyl)phosphine oxide,tri(2-ethyl-3-decyl-1-aziridinyl)phosphine sulfide, and the like.

The multialdehyde coupling agents are represented by compounds such as1,4,7-naphthalenetricarboxyaldehyde, 1,7,9-anthracenetricarboxyaldehyde,1,3,5-pentanetricarboxyaldehyde, and similar multialdehyde-containingaliphatic and aromatic compounds. The multiketones are represented bycompounds such as 1,4,9,10-anthracenetetrone,2,3-diacetonylcyclohexanone, and the like. Examples of themultianhydrides include pyromellitic dianhydride, styrene-maleicanhydride copolymers, and the like. Examples of the multiesters includediethyladipate, triethylcitrate, 1,3,5-benzenetricarboxylic acid,triethyl ester, and the like.

Among the multihalide coupling agents are the silicon tetrahalides suchas silicon tetrachloride, silicon tetrabromide, and silicon tetraiodide;the trihalosilanes such as trichlorosilane, trichloroethylsilane,tribromobenzylsilane, and the like; and the multihalogen-substitutedhydrocarbons, such as 1,3,5-tri(bromomethyl)benzene,2,5,6,9-tetrachloro-3,7-decadiene, and the like, in which the halogen isattached to a carbon atom which is alpha to an activating group such asan ether linkage, a carbonyl group, or a carbon-to-carbon double bond.Substituents inert with respect to lithium atoms in the terminallyreactive polymer can also be present in the active halogen-containingcompounds. Alternatively, other suitable reactive groups different fromthe halogens as described above can be present.

Other metal multihalides, particularly those of tin, lead, or germanium,can be employed as coupling and branching agents. Silicon or other metalmultialkoxides, such as silicon tetraethoxide, are also suitablecoupling agents.

Examples of compounds containing more than one type of functional groupinclude 1,3-dichloro-2-propanone, 2,2-dibromo-3-decanone,2,4-dibromo-3-pentanone, 1,2; 4,5-diepoxy-3-pentanone, 1,2;4,5-diepoxy-3-hexanone, 1,2; 11,12-diepoxy-8-pentadecanone, 1,2;18,19-diepoxy-7,14-eicosanedione, and the like.

Useful multifunctional coupling agents include epoxidized vegetable oilssuch as epoxidized soybean oil, epoxidized linseed oil and the like ormixtures thereof.

The presently preferred coupling agent is epoxidized vegetable oil.Presently preferred is epoxidized soybean oil.

Process

The unique polymodal tapered block character of the polymer and lowblueness and good impact strength and/or ductility of articles made fromthe polymer or blends of the polymer of the first embodiment of thisinvention are produced by the unique sequence of an initial charge ofmonovinylaromatic monomer and initiator and a subsequent addition of asecond charge of initiator and monovinylaromatic monomer, followed by aseparate charge of a mixture of monovinylaromatic monomer and conjugateddiene, and a subsequent coupling step

The unique polymodal tapered block character of the polymer and lowblueness and good impact strength and/or ductility of articles made fromthe polymer or blends of the polymer of the second embodiment of thisinvention are produced by the process of the first embodiment with theaddition of a second separate charge of a mixture of monovinyl aromaticand conjugated diene monomers next preceeding the coupling step.

In each of the two embodiments of this invention the first initiatorcharge produces active living monovinyl aromatic component polymerblocks with alkali metal atoms (from the initiator) on at least one endto form active reaction sites. Each subsequent monomer charge addsmonomer to the living polymer chain at the alkali metal reaction site.At each stage of charging, polymerization is allowed to continue untilessentially no free monomer is present.

With each subsequent charge which includes initiator a newpolymer-alkali metal species will be produced, and each subsequentmonomer charge has an opportunity for polymerization of part of thecharge with each of the existing polymer-alkali metal species. Each ofthe active living polymer chains will be terminated on both ends withmonovinyl aromatic blocks after polymerization of each monomer chargecontaining monovinyl aromatic. When mixtures of monovinyl aromaticmonomer and conjugated diene are charged, the polymer chains will beterminated with the monovinyl aromatic rich ends of the tapered blocksprior to coupling. After virtually complete polymerization of the finalmonomer charge, the active living linear block copolymers are chargedwith a difunctional or polyfunctional coupling agent to allow couplingof each of the living species with each of the other living species orwith others of the same living species to form the desired polymodaltapered block copolymers. If the coupling agent is not 100 percentefficient and/or if less or more than a stoichiometric amount ofcoupling agent is used, there can be some uncoupled terminated polymerchains of each of the species in the final reaction mixture.

Use of difunctional coupling agents will produce predominantly linearpolymer chains. Depending upon functionality, various degrees and kindsof branching may be accomplished with polyfunctional coupling agents.Variations in the amount of a particular polyfunctional coupling agentalso can be used to manipulate the degree and kind of branching at thecoupling sites.

The charging sequences of this invention and the resulting polymers ateach stage are exemplified using a selected monovinylaromatic monomer,conjugated diene and polyfunctional coupling agent in the followingTables 1 and 2.

TABLE 1 Invention Charging Sequence (First Embodiment) Charge Contentsof Charge Resulting Polymer Chains (a) randomizer, initiator₁ S₁-L₁ andstyrene₁ (b) initiator₂ and styrene₂ S₁-S₂-Li₁ S₂-Li₂ (c) butadiene₁ andstyrene₃ S₁-S₂-B₁/S₃-Li₁ S₂-B₁/S₃-Li₂ (d) coupling agent polymodaltapered block copolymers with styrene terminal blocks

where

S =styrene

B=butadiene

B/S=tapered block

Li=residue from a monoalkali metal initiator remaining on the end of thepolymerization chain or reaction site prior to termination or coupling.

subscripts=designation of the numerical order in which that particularcomponent was charged or formed.

TABLE 2 Invention Charging Sequence (First Embodiment) Charge Contentsof Charge Resulting Polymer Chains (a) randomizer, initiator₁ S₁-L₁ andstyrene₁ (b) initiator₂ and styrene₂ S₁-S₂-Li₁ S₂-Li₂ (c) butadiene₁ andstyrene₃ S₁-S₂-B₁/S₃-Li₁ S₂-B₁/S₃-Li₂ (d) butadiene₂ and styrene₄S₁-S₂-B₁/S₃-B₂/S₄-Li₁ S₂-B₁/S₃-B₂/S₄-Li₂ (e) coupling agent polymodaltapered block copolymers with styrene terminal blocks

where

S=styrene

B=butadiene

B/S=tapered block

Li=residue from a monoalkali metal initiator remaining on the end of thepolymerization chain or reaction site prior to termination or coupling.

subscripts =designation of the numerical order in which that particularcomponent was charged or formed.

The randomizer is usually added with the diluent initially charged tothe reactor. Each of the charges which has two monomers may be either amixture of the two monomers or simultaneous charging of two separatemonomers.

As can be seen from the intermediate products listed in the chargingsequence tables above, in two embodiments of the invention there are atleast two distinct species of polymer chains before coupling. Thus,polymodal tapered block copolymers comprising relatively high and lowmolecular weight species can be produced.

Tapered blocks in each of the growing polymer chains are produced bysimultaneously charging with at least two monomers as shown in thepreceeding tables of the inventive charging sequences.

The randomizer regulates tapering or random polymerization of themonovinylaromatic monomer and the conjugated diene in a mixed monomercharge. Choice of randomizer can be used to manipulate the direction oftaper in blocks resulting from charges of mixtures of monomers. Thetaper can be either a graduation from conjugated diene rich chain tomonovinylaromatic rich chain or a graduation from a monovinylaromaticrich chain to conjugated diene rich chain according to which monomerenters the chain faster. For example, when tetrahydrofuran is used as arandomizer, the diene enters into the chain faster than the monovinylsubstituted aromatic; therefore, when both the monovinylaromatic monomerand the conjugated diene are present, the block tapers gradually from anessentially polybutadiene block to an essentially monovinyl substitutedaromatic polymer block.

The weight ratio of monovinyl substituted aromatic monomer to conjugateddiene monomer in each of the tapered blocks is from about 1:0.63 toabout 1:2, preferably from about 1:0.67 to about 1:1.8, and morepreferably from about 1:0.8 to about 1:1.5. The weight ratios ofmonovinyl substituted aromatic monomer to conjugated diene monomer ineach of the tapered blocks in the same polymer chain do not have to bethe same. See Example VII.

Generally each of the two tapered blocks made in steps (c) and (d) ofthe second embodiment of this invention can be of equal size; however,actual sizes of the two tapered blocks can vary within the samecopolymer depending upon the amounts of monomers charged in each of thethird and fourth monomer charges. See run 13 in Example VII.

Prior to coupling, all of the living polymer chains havemonovinylaromatic terminal blocks on one end because of the initialmonovinylaromatic charge (a) and charge (b) made with initiator; theliving ends of the chains will have tapered blocks prior to couplingbecause of the charge containing both monovinylaromatic and conjugateddiene monomers made next preceeding the coupling step.

In addition to the sequence of additions of the monomers and of theinitiator, it is important to control the amount of each monomer andinitiator addition at each stage or increment so that a suitableproportion of block sizes and proportion of polymodality is obtained.

Generally in a presently preferred first embodiment of this invention,if a polymer which is about 75 weight percent monovinylaromatic, basedon total monomer weight, is used, from about 27 to about 80 weightpercent of the total monovinylaromatic monomer is charged in step (a),from about 5 to about 21 weight percent of the total monovinylaromaticmonomer is charged in step (b), and from about 20 to about 60 weightpercent of the total monovinylaromatic monomer is charged in step (c).Generally more preferably, from about 40 to about 70 weight percent ofthe total monovinylaromatic monomer is charged in step (a), from about 8to about 19 weight percent of the total monovinylaromatic monomer ischarged in step (b), and from about 27 to about 40 weight percent of thetotal monovinylaromatic monomer is charged in step (c). Generallypresently most preferably, from about 47 to about 60 weight percent ofthe total monovinylaromatic monomer is charged in step (a), from about11 to about 16 weight percent of the total monovinylaromatic monomer ischarged in step (b), and from about 29 to about 37 weight percent of thetotal monovinylaromatic monomer is charged in step (c).

Generally in a presently preferred second embodiment of this invention,if a polymer which is about 75 weight percent monovinylaromatic, basedon total monomer weight, is used, from about 27 to about 80 weightpercent of the total monovinylaromatic monomer is charged in step (a),from about 5 to about 21 weight percent of the total monovinylaromaticmonomer is charged in step (b), from about 3 to about 19 weight percentof the total monovinylaromatic monomer is charged in step (c), and fromabout 13 to about 36 weight percent of the total monovinylaromaticmonomer is charged in step (d). Generally more preferably, from about 40to about 67 weight percent of the total monovinylaromatic monomer ischarged in step (a), from about 8 to about 19 weight percent of thetotal monovinylaromatic monomer is charged in step (b), from about 5 toabout 19 weight percent of the total monovinylaromatic monomer ischarged in step (c), and from about 16 to about 32 weight percent of thetotal monovinylaromatic monomer is charged in step (d). Generallypresently most preferably, from about 47 to about 60 weight percent ofthe total monovinylaromatic monomer is charged in step (a), from about11 to about 16 weight percent of the total monovinylaromatic monomer ischarged in step (b), from about 8 to about 13 weight percent of thetotal monovinylaromatic monomer is charged in step (c), and from about20 to about 25 weight percent of 'the total monovinylaromatic monomer ischarged in step (d).

In either of the two embodiments of this invention it is feasible tostretch out over an interval of time the addition of one or more of theincrements of initiator, thus spreading (increasing) further thepolymodality of the resulting product upon coupling.

The polymerization process is carried out in a hydrocarbon diluent a tany suitable temperature in a range of about −10° to about 150° C.,preferably in the range of about 0° to about 110° C., at pressuressufficient to maintain the reaction mixture substantially in the liquidphase. Temperatures and pressures will peak during polymerization ofeach monomer charge and then decrease when essentially no free monomeris left to re act. Appropriate hydrocarbon diluents include linear andcycloparaffins such as butane, pentane, bexane, octane, cyclohexane,cyclopentane and mixtures thereof. Presently preferred is cyclohexane.Generally the choice of hydrocarbon or hydrocarbon mixture and thetemperature is such that the resulting polymer is in solution.

Small amounts of polar compounds are used to improve the effectivenessof alkylmonoalkali metal initiators such as n-butyllithium; dissociationof the alkylmonoalkali metal initiator. affects the rate of initiationand polymerization. The polar compounds also effect partialrandomization of the vinylarene/conjugated diene so as to increase therandom portion of the tapered block. The polar compounds are generallyused in admixture with the hydrocarbon diluent.

The amounts of polar compounds used as randomizers and promoters ofeffectiveness of initiators in this invention will vary according to thereactivity and effectiveness of the particular randomizer used. Forexample, 1,2-dimethoxyethane, tetramethylethylenediamine and1,2-dimethoxybenzene are much more efficient randomizers than most ofthe others listed above when used with the particular initiators andmonomers used in the invention runt s described below. However,tetrahydrofuran is often used because the reaction will go nearer tocompletion in a shorter time after the initial reaction in the monomerrich environment. Also, there are dramatic variations in the amounts ofeach of these most efficient randomizers which will be needed. Forexample, for polymerizations such as those shown in the examples ofinvention runs in Example I of this application, about three and a halftimes as much tetrahydrofuran as 1,2-dimethoxyethane would be needed.

The amounts of polar compounds used as randomizers will also varyaccording to the desired molecular structure of the portions of taperedblocks which result from conjugated diene addition. For example, whenusing tetrahydrofuran, and 1,4 addition in excess of 1,2 addition isdesired, smaller amounts of the tetrahydrofuran would be used. In thisexample, when it is desirable that the tapered blocks of the polymerhave more nearly equal amounts of 1,4 addition of butadiene and 1,2addition of butadiene or only a little more 1,4 addition than 1,2addition of butadiene, more of the tetrahydrofuran can be used.

When polymers with higher vinyl character resulting from 1,2 addition inexcess of 1,4 addition are desired, then the useful amounts oftetrahydrofuran needed would be larger. However, use of too muchrandomizer can result in excessive polymer-lithium termination duringpolymerization and/or poor stability of the polymer and/or undesired,side reactions, depending upon choice of randomizer. Use of too littlerandomizer would result in inefficient initiator use, compositionalvariations and broader molecular weight distribution.

The initial monovinylaromatic charge is made with the randomizer presentfor the additional effect of causing the monovinylaromatic componentresulting from each initiator charge to be of relatively narrowmolecular weight distribution. In the two embodiments of this invention,by varying the amounts of initiator in each of the two charges havinginitiator, the differences in molecular weights of the monovinylaromaticcomponents resulting from each of the two charges can be increased.

In each of the two embodiments of the invention, amounts of initiatoremployed are those which will produce resins with desirable melt flowwhich can be used in blends to make articles with a good balance ofproperties including minimal blueness, and good impact strength and/orductility. Presently preferred when making invention polymers to be usedin blends are amounts of initiator in each of the two initiator chargessufficient to obtain a block copolymer having a melt flow in the rangefrom about 2 to about 50 g/10 minutes, more preferably from about 4 toabout 30 g/10 minutes, and most preferably from about 7 to about 20 g/10minutes, as determined by ASTM D1238-73, condition 200/5.0. The amountsof initiator contemplated as useful in each of the two charges havinginitiator are shown in Tables 3 and 4.

Use of too small an amount of initiator would result in high molecularweight polymers. Conversely, use of too large an amount of initiatorwould result in polymers having short chain polymeric species and lowmolecular weight.

The weight ratio of the amounts of initiator in each of the chargeshaving initiator can be represented as 1:0.25-300.

Li₁:Li₂::1:0.25-300

wherein

Li₁=initiator in the first charge

Li₂=initiator in the second charge

More preferably for most applications, the amount of initiator in thesecond charge of initiator is from about 0.3 to about 10 times, based onweight, as much as the amount of initiator in the first initiatorcharge. Generally, presently most preferably, the amounts of initiatorsare selected such that the amount in the second charge is at least equalto or larger than that employed in the first charge.

Varying the weight ratios of amounts of the initiator charges willresult in variations of the proportionate amounts of specie s present inthe copolymer. Other factors affecting the proportionate amounts ofspecies present in the copolymer include presence of impurities and/orscavengers in the reactor, effectiveness of the polar randomizer as apromoter and choice of coupling agent(s).

The polymerization is carried out in a substantial absence of oxygen andwater, preferably under an inert gas atmosphere. Prior to the couplingstep, the reaction mass contains a very high percentage of molecules(polymer chains) in which an alkali metal cation is positioned at oneend of each polymer chain. Impurities in the feed such as water oralcohol reduce the amounts of monoalkali metal polymer in the reactionmass.

After essentially complete polymerization of the final charge added tothe polymer, one or more suitable difunctional or polyfunctionalcoupling agents is added. As used here, the term “coupling” means thebringing together and joining, by means of one or more central couplingatoms or coupling moieties, two or more of the living monoalkalimetal-terminated polymer chains. A wide variety of compounds for suchpurposes can be employed.

Any effective amount of the coupling agent can be employed While theamount is not believed to be particularly critical, a stoichiometricamount relative to the active polymer-alkali metal tends to promotemaximum coupling as a generality. Presently preferred is an amount ofcoupling agent slightly greater than stoichiometric relative to theactive polymer-alkali metal. However, less than stoichiometric amountscan be used for higher degrees of coupling where desired for particularproducts of broadened molecular weight distribution.

Typically, in each of the embodiments of this invention, the totalamount of coupling agent is in the range of about 0.005 to 10 phm (partsper 100 parts of total monomers employed in the polymerization).Preferred when most combinations of monomers and coupling agents areused to practice this invention is about 0.2 to about 0.6 phm ofcoupling agent, depending on amounts of initiator used. Presently mostpreferred is about 0.3 to about 0.5 phm, depending upon amounts ofinitiator used. Use of an amount of a reasonably highly efficientcoupling agent within these ranges provides polymers with a moderatelyabroad molecular weight distribution that has proven useful to custommolders. Use of an insufficient amount of coupling a gent will result inless complete coupling of the living polymer chains and, depending uponchoice of coupling agent, more branching; use of an excessive amount ofcoupling agent will also result in more uncoupled chains.

At the conclusion of the coupling process, the coupled polymer may stillcontain bound polymeric alkali metal alkoxides depending on the type ofcoupling agent employed. The system is treated with an active compoundsuch as water, alcohol, phenols, carbon dioxide or linear saturatedaliphatic mono- and dicarboxylic acids to remove any remaining alkalimetal from the copolymer chain.

While the polymer product is still in solution stabilization agents canbe added. Additional stabilizers could be added during finishing beforepelletizing. This treatment will provide oxidative stability for thepolymer during processing and handling and subsequent long term use bythe customer.

Commonly used stabilization processes can use a combination of compoundswhich include, but are not limited to, a hindered phenol and anorganophosphite, particular examples of which are octadecyl3-(3′,5′-di-t-butyl-4′-hydroxyphenyl) propionate andtris-nonylphenylphosphite.

After stabilization, the hydrocarbon diluent is then flashed from thepolymer solution to increase the solids content. The polymer cement,i.e., the polymer in the polymerization solvent, usually contains about10 to 40, more usually 20 to 35, weight percent solids, the balancesolvent. Preferably, but not necessarily, the polymer cement is flashedto remove by evaporation a portion of the solvent so as to reduce thesolvent content to a concentration of about 0 to 50, more usually about0 to 10, weight percent (corresponding to a solids content of about 100to 50, more usually about 100 to 90, weight percent).

Flashing of the polymer cement may be followed by desolventizingextrusion with vacuum in commercial production or by other vacuumingprocesses to achieve consistent solvent content of less than 0.3 weightpercent.

The resinous copolymeric products can be, and normally are, compoundedwith anti-oxidants, anti-blocking agents, release agents and otheradditives, as known in the compounding arts.

Typical charging sequences and useful ranges of amounts of the chargesfor each of the two embodiments of this invention are given in Tables 3and 4.

TABLE 3 Ranges of Amounts of Components in a Typical Invention ChargingSequence^(a) (First Embodiment) Step Component^(b) Broad Range^(c)Preferred Range^(c) More Preferred Range^(c) (a) randomizer^(d)0.001-0.10  0.005-0.085 0.015-0.060 initiator 0.005-1.5  0.01-0.1 0.01-0.05 and monovinylarene 20-60 30-50 35-45 monomer (b) initiator0.005-1.5  0.01-1.0  0.02-0.1  and monovinylarene  4-16  6-14  8-12monomer (c) monovinylarene 15-45 20-30 22-28 monomer and conjugateddiene 15-45 20-30 22-28 monomer (d) coupling agent 0.005-10   0.2-0.60.3-0.5 ^(a)Charges of monomer and initiator are made in the presence ofan amount of diluent or solvent sufficient to prevent excessive heat ofreaction. ^(b)Monomers within each charge having more than one monomercan be added simultaneously or as a mixture, slowly or quickly.Randomizer in charge (a) may be already present in the diluent or addedas a separate charge. ^(c)Ranges of amounts are given in parts by weightper 100 parts by weight of total monomers (phm). ^(d)For amounts ofrandomizer, refer to the following discussion of randomizers. To achievehigh vinyl content, up to 3 phm randomizer may be used.

TABLE 4 Ranges of Amounts of Components in a Typical Invention ChargingSequence^(a) (Second Embodiment) Step Component^(b) Broad Range^(c)Preferred Range^(c) More Preferred Range^(c) (a) randomizer^(d)0.001-0.10  0.005-0.085 0.015-0.60  initiator 0.005-1.50  0.01-0.1 0.04-0.08 and monovinylarene 20-60 30-50 35-45 monomer (b) initiator0.005-1.5  0.01-1.0  .03-.07 and monovinylarene  4-16  6-14  8-12monomer (c) monovinylarene  2-14  4-12  6-10 monomer and conjugateddiene  2-13  3-11 5-9 monomer (d) monovinylarene 10-27 12-24 15-19monomer and conjugated diene  8-28 13-23 16-20 monomer (e) couplingagent 0.005-10   0.2-0.6 0.3-0.5 ^(a)Charges of monomer and initiatorare made in the presence of an amount of diluent or solvent sufficientto prevent excessive heat of reaction. ^(b)Monomers within each chargehaving more than one monomer can be added simultaneously or as amixture, slowly or quickly. Randomizer in charge (a) may be alreadypresent in the diluent or added as a separate charge. ^(c)Ranges ofamounts are given in parts by weight per 100 parts by weight of totalmonomers (phm). ^(d)For amounts of randomizer, refer to the followingdiscussion of randomizers. To achieve high vinyl content, up to 3 phmrandomizer may be used.

After coupling at least the coupled and uncoupled polymeric speciesshown in Tables 5 and 6 are present in the polymodal polymers of thefirst and second embodiments respectively, of this invention.

TABLE 5 Polymeric Species Included in First EmbodimentS₁-S₂-B₁/S₃-x-S₃/B₁-S₂-S₁ S₁-S₂-B₁/S₃-x-S₃/B₁-S₂ S₂-B₁/S₃-x-S₃/B₁-S₂S₂-B₁/S₃ S₁-S₂-B₁/S₃

S=monovinylaromatic block

B=conjugated diene block

B/S=tapered block

x=residual coupling agent or coupling site

subscripts=indications of the charges which were the source of thepolymer blocks.

TABLE 6 Polymeric Species Included in Second EmbodimentS₁-S₂-B₁/S₃-B₂/S₄-x-S₄/B₂-S₃/ B₁-S₂-S₁S₁-S₂-B₁/S₃-B₂/S₄-x-S₄/B₂-S₃/B₁-S₂ S₂-B₁/S₃-B₂/S₄-x-S₄/B₂-S₃/B₁-S₂S₂-B₁/S₃-B₂/S₄ S₁-S₂-B₁/S₃-B₂/S₄

S=monovinylaromatic block

B=conjugated diene block

B/S=tapered block

x=residual coupling agent or coupling site

subscripts=indications of the charges which were the source of thepolymer blocks.

In each of the embodiments depending upon choice and amount of couplingagent or agents and whether coupling agents are charged as a mixture orincrementally, there can be present other polymeric species with varyingdegrees of branching.

Blends

The resinous polymodal copolymer products of this invention can beblended with other polymers such as acrylonitrile-butadiene-styrenecopolymers (ABS), styrene-acrylonitrile copolymers (SAN), and otherstyrene copolymers. When less transparency is desired or transparency isnot necessary, the invention copolymers can be blended with polyolefinsand/or olefin copolymers.

Blends of the invention polymers with polymers of styrene areparticularly useful applications for the improved tapered blockcopolymers of this invention. Articles made from these blends havesurprisingly low blueness and advantageous impact strength and/orductility. For example, articles made from styrene homopolymer andeither of the two embodiments of this invention typically have Hunternegative b blueness values of less than 20, most often less than 18.Thus, less of the invention copolymer is needed to achieve low bluenessin articles made from blends with styrene homopolymers than would beneeded of other comparative polymodal monovinylaromatic-conjugated dieneblock copolymers.

The presently preferred polymers of styrene employed in the blends ofthis invention are usually (a) homopolymers of styrene; or (b)copolymers of styrene as a major component with a minor amount, e.g., upto 20 weight percent, of any other copolymerizable monovinyl aromaticcompound other than styrene, such as alpha-methylstyrene, vinyltolueneor para-tertiary-butyl styrene. A minor amount, e.g., up to 20 weightpercent, of other monomers such as methyl acrylate, methyl methacrylate,acrylonitrile and the like can be copolymerized with the styrene.

The invention copolymers can be blended with styrene resins made in bulkpolymerization. These resins are commonly prepared by heating styreneand any comonomer at temperatures in the range of 100° to 200° C. withapplication of pressure, if necessary, to combine the monomers. Thepolymerization can also be carried out at lower temperatures by theaddition of free-radical generating peroxidic catalysts such as benzoylperoxide, acetyl peroxide, di-t-butyl peroxide and the like.Alternatively, the polymerization can be carried out in suspension toyield a dry powder or in emulsion, usually resulting in a latex ofpolystyrene which can be coagulated to yield the solid powderypolystyrene. The polymerization can also be carried out in solution withprecipitation of the product, if desired. Solvent can be removed bystandard techniques such as steamstripping or solvent evaporation.

High impact polystryene (HIPS) also can be successfully employed inblends with the invention copolymers. Suitable high impact polystyrenescan be prepared by polymerizing styrene in the presence of an elastomer,typically polybutadiene rubber. In these resins the styrene forms acontinuous phase throughout which the rubber particles are dispersed.

The blends of this invention can be prepared by any suitable meansincluding blending, tumbling and extrusion. Examples of these methodsinclude, but are not limited to, dry mixing in the form of a powder orpellets, wet mixing in the form of a solution or slurry, and meltextrusion compounding.

The polymers and any other ingredients or additives way be mechanicallyblended together in the desired proportions with the aid of any suitablemixing device conveniently used for mixing rubbers or plastics, such as,for example, a differential roll mill, a Banbury mixer, or an extruder.

In these types of blending methods the polymers and any other componentsand additives used can be in any form, such as, for example, fluff,powder, granulate, pellet, solution, slurry, and/or emulsion. Anyadditive can be combined with the polymers according to any method knownin the art. Examples of incorporation methods include, but are notlimited to, dry mixing in the form of a powder and wet mixing in theform of a solution or slurry.

Melt extrusion compounding can be carried out using any suitable methodsuch as in single screw or twin screw extruders or other melt extrudersat temperatures above the melting point or glass transition temperatureof the polymers.

The presently preferred method comprises blending the polymers in powderor granulate form and extruding the blend in sheet form to feed athermoforming or direct feed to an injection or blow molder.

In order to facilitate thorough mixing of the polymers and to developthe desired combination of physical properties, pellets are generallymetered by loss-in-weight feeders or by screw feeders at a temperaturelow enough to avoid softening the pellets. The metered pellets aredropped into an extruder which melts and blends the components toprovide a homogenous melt.

Alternatively, solution blending methods known in the art may be used.

The ranges of amounts of polymers useful in blends varies according tothe properties and economics required. For example, when an inventioncopolymer is blended with a polymer of styrene, practical ranges includeusing amounts such as from about 10 to about 70 weight percent polymerof styrene, more usually from about 20 to about 65 weight percentpolymer of styrene, and most preferably from about 30 to about 60 weightpercent polymer of styrene with the balance being one or more of thepolymodal resinous copolymer products of this invention. For a moreparticular example, when the invention copolymers are blended withgeneral purpose polystyrene, broad ranges include using amounts such asfrom about 10 to about 70 weight percent polystyrene, more usually fromabout 20 to about 65 weight percent polystyrene, and most preferablyfrom about 30 to about 60 weight percent polystyrene with the balancebeing one or more of the polymodal resinous copolymer products of thisinvention. Generally, use of too much of the invention copolymers in ablend would result in good properties but loss of economic advantage.Use of too little of the invention copolymers in a blend would result inloss of impact resistance. These blends can be economical ways ofgaining the desirable attributes of both polystyrene and the inventionpolymers while maintaining low blueness in articles made from theblends.

The compositions of this invention or blends thereof can be extruded,thermoformed, injection molded, blow molded, or made into films orsheets. Articles made from the compositions of this invention aretransparent with low blueness, have good impact strength and have otherphysical properties within acceptable ranges for such applications asdrinking cups, lids, bottles, other food containers, medical drainageunits, shrink wrap and over wrap. Articles made from blends of thecopolymers of this invention can economically provide advantageousproperties for similar applications.

Test Procedures

The blend blueness values were determined on a Hunter Lab colormeterModel D 25 using the Hunter Lab procedure. Blueness values are expressedas −b, where larger absolute numbers indicate more blueness.

Other properties were tested using ASTH procedures as shown in Table 7.

TABLE 7 Test Procedures Used Property ASTM Method Flow rate, g/10 min D1238-88 Condition 200/5.0 Haze, % D 1003-61 (1990) Transmittance, % D1003-61 (1990) Shore D hardness D 2240-91 Tensile strength at yield andD 638-91 at 50 mm/min break, MPa Type I test specimens Elongation atyield and break, % D 638-91 at 50 mm/min Flexural modulus, HPa D 790-86Izod impact strength, D 256-88 notched, J/m Vicat softening point, ° C.D 1525-91 Total energy dart drop, J D 4272-85

EXAMPLES

The following examples will describe in more detail the experimentalprocess used and the polymodal tapered block copolymers with vinylareneterminal blocks obtained as a result of the process and blends made withthe invention copolymers. These examples should be taken as illustrativeand not restrictive.

Styrene and butadiene were chosen as monomers to exemplify theinvention, and randomizer, initiator, coupling agent and diluentappropriate for these monomers were used. Quantities of reagents areusually expressed in parts per hundred monomer (phi) based on the totalweight of monovinylarene and conjugated diene employed.

Example I

This example describes four invention polymerization runs (1, 2, 3, 4)that were carried out to produce resinous polymodal, coupled,, taperedblock styrene-butadiene copolymers with resinous terminal blocks. Theseruns exemplify the first embodiment of the invention. Styrene (fromStirling Chemical) and 1,3-butadiene (from Texas El Paso) were dried bypassage over activated alumina (Kaiser A-201), and then copolymerizedand coupled in a 4-stage process using n-butyllithium initiator (fromLithium Corporation of America).

Polymerization runs were carried out under nitrogen in a stirred,jacketed, stainless steel 7.6-liter reactor employing essentiallyanhydrous reactants and conditions. The anhydrous mixtures were stirredcontinuously during the polymerization process. The cyclohexane diluent,which contained 0.04 phm tetrahydrofuran (THF) in each polymerization inthis example, was preheated to about 50° C. before monomers were chargedto the reactor. The n-butyllithium was charged as a 2 weight percentsolution in cyclohexane. In the polymerization step in which bothbutadiene and styrene were charged, they were charged simultaneously asa mixture.

In the coupling step, the Vikoflex® 7170 coupling agent used was anepoxidized vegetable oil commercially available from Viking ChemicalCompany. In the terminating step, carbon dioxide from a pressurizedcontainer was admitted to provide about 0.4 phm carbon dioxide to thereactor. Water was also added in an amount slightly in stoichiometricexcess of the initiator to separate the lithium residues from thepolymer chains.

The antioxidant mixture added in the stabilizing step contained ahindered phenol [octadecyl 3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate, commercially available as Irganox® 1076 from Ciba-Geigy] andan organic phosphate (trisnonylphenyl phosphate, available as TNPP fromGE Specialty Chemicals). Each stabilizer was dissolved separately incyclohexane and mixed together. Enough of the mixture was added to thereactor to provide 0.25 phm hindered phenol and 1 phm organic phosphate.In Runs 1 and 2 a microcrystalline wax (BE Square® 195) was also addedas an antiblocking agent.

After each addition of monomer, initiator or additive, the feed lineswere rinsed with approximately 10-20 phm cyclohexane solvent and clearedwith a nitrogen sparge.

Following the stabilization step, each copolymer solution was flashed at178-180° C. to remove a portion of the diluent. Substantially all of theremaining diluent was removed in a vacuum oven by drying at 90° C. forone hour. The resulting polymer was chopped in a granulator into crumbsize and then dried for an additional hour in a vacuum oven.

In each of the four runs (1, 2, 3, and 4), 1500 g total monomers(butadiene and styrene) were used. About 76 weight percent of the totalamount of cyclobexane diluent (3130 g) was charged initially. Theremaining cyclohexane diluent was added during the run as a diluent orflush for the various reactants added in subsequent steps. In these fourpolymerizations, the weight ratio of total monomers charged was 75/25styrene/butadiene.

The charges and the results of the runs are summarized in Table 8.Tapered butadiene/styrene blocks were formed in step 3 by charging bothbutadiene and styrene monomers. The charging sequence used was i, S₁, i,S₂, B₁/S₃, coupling agent. The monomer ratios corresponding to the S₁,S₂, B₁/S₁ sequence were 40, 10, 25/25. Weight ratios of amounts ofinitiator used in the first two steps of each of the four runs was keptconstant at 1:1, but the amounts were decreased from 0.08 phm in run 1to 0.055 phm in run 4 to provide a series of decreasing melt flowresins.

The devolatilized copolymers from runs 1, 2, 3, and 4 were designatedinvention copolymers 1, 2, 3 and 4, and had melt flows of 39.1 g/10 min,19.0 g/10 min, 9.0 g/10 min and 4.8 g/10 min, respectively. Thedifferences in melt flows were attributable to differences in amounts ofinitiator used in each of the four runs.

TABLE 8 Invention Runs - First Embodiment Components^(a) Run 1 Run 2 Run3 Run 4 Step 1 Cyclohexane, phm 145 145 145 145 Tetrahydrofuran, phm0.04 0.04 0.04 0.04 n-Butyllithium initiator, phm 0.08 0.07 0.06 0.055Styrene, phm 40 40 40 40 Polymerization Time, min 12 12 12 12 PeakPolymerization 82 81 85 85 Temperature, ° C. Step 2 n-Butyllithiuminitiator, phm 0.08 0.07 0.06 0.055 Styrene, phm 10 10 10 10Polymerization Time, min 12 12 12 12 Peak Polymerization Temperature, °C. 67 70 71 70 Step 3 Butadiene, phm 25 25 25 25 Styrene, phm 25 25 2525 Polymerization Time, min 16 16 16 16 Peak Polymerization 122 122 122116 Temperature, ° C. Step 4 (Coupling) Vikoflex 7170, phm 0.4 0.4 0.40.4 Time, min 16 16 16 16 Temperature, ° C. 94 93 90 93 Step 5(Terminating) Water, phm 0.2 0.2 0.2 0.2 Carbon Dioxide, phm 0.4 0.4 0.40.4 Time, min 25 25 25 25 Temperature, ° C. 80 93 87 81 Step 6(Stabilizing) Stabilizer Mixture, phm 1.25 1.25 1.25 1.25 BE Square wax0.15 0.15 0.15 0.15 Time, min 5 5 5 5 Temperature, ° C. n.a. n.a. 84n.a. Recovered Resin Melt Flow, g/10 min 39.1 19.0 9.0 4.8 Mw/Mn,thousands 105/63 108/53 128/65 143/91 Heterogeneity Index 1.67 2.05 1.971.57 ^(a)After each addition of monomer, initiator or additive, the feedlines were rinsed with approximately 5-20 phm cyclohexane diluent andcleared with nitrogen.

Example II

Three more polymerization runs were carried out according to the firstembodiment of the present invention to demonstrate the effects ofvarying the weight ratio of amounts of initiator in each of the twoinitiator charges. The charges and results of the runs are shown inTable 9. Again, the weight ratio of styrene to butadiene charged was 75to 25. Samples were made with i, S₁, i, S₂, B₁/S₃ addition sequencefollowed by coupling; monomer ratios of 40, 10, 25/25 were used.

In each of the three runs of this example, 0.03 phm initiator wascharged in the first step. The amount of initiator charged in the secondstep was varied from 0.08 phm (run 5) to 0.095 phm (run 7) for a rangeof ratios of amount of initiator in first step to amount in second stepfrom 1:2.7 (run 5) to 1:3.2 (run 7).

Copolymers from runs 5, 6 and 7 were devolatilized to form inventioncopolymers 5, 6 and 7, which had melt flows of 5.0 g/10 min, 5.4 g/10min, and 7.1 g/10 min, respectively.

TABLE 9 Invention Runs - First Embodiment Components^(a) Run 5 Run 6 Run7 Step 1 Cyclohexane, phm 145 145 145 Tetrahydrofuran 0.04 0.04 0.04n-Butyllithium 0.03 0.03 0.03 initiator, phm Styrene, phm 40 40 40Polymerization Time, min 12 12 12 Peak Polymerization 77 79 76Temperature, ° C. Peak Polymerization Pressure, psi Step 2n-Butyllithium 0.08 0.085 0.095 initiator, phm Styrene, phm 10 10 10Polymerization Time, min 12 12 12 Peak Polymerization 64 71 65Temperature, ° C. Step 3 Butadiene, phm 25 25 25 Styrene, phm 25 25 25Polymerization Time, min 16 16 16 Peak Polymerization 117 121 111Temperature, ° C. Step 4 (Coupling) Vikoflex 7170, phm 0.4 0.4 0.4 Time,min 16 16 16 Temperature, ° C. 88 87 89 Step 5 (Terminating) Water, phm0.2 0.2 0.2 Carbon Dioxide, phm 0.4 0.4 0.4 Time, min 25 25 25Temperature, ° C. 82 82 84 Step 6 (Stabilizing) Stabilizer Mixture, phm1.25 1.25 1.25 BE Square wax 0.15 0.15 0.15 Time, min 5 5 5 RecoveredResin Melt Flow, g/10 min 5.0 5.4 7.1 Mw/Mn, thousands 181/114 177/111138/93 Heterogeneity Index 1.6 1.6 1.69 ^(a)After each addition ofmonomer, initiator or additive, the feed lines were rinsed withapproximately 5-20 phm cyclohexane diluent and cleared with nitrogen.

Example III

To demonstrate the second embodiment of this invention, three morepolymerization runs were carried out according to the proceduresdescribed in Example I, with the exception that the sequences andamounts of charges were as shown in Table 10. Tapered butadiene/styreneblocks were formed in the third and fourth steps by charging a mixtureof butadiene and styrene monomers. The monomer addition sequence was i,S₁, i, S₂, B₁/S₃, B₂/S₄ followed by coupling; the monomer weight ratioswere 40, 10, 12.5/12.5, 12.5/12.5, respectively. The polymers were 75percent styrene and 25 percent butadiene.

In each of the three runs of this example the weight ratio of amount ofinitiator in the first step to the amount in the second step was keptconstant at 1:1 with the absolute amount varied from 0.05 phm (run 9) to0.06 phm (run 8).

The copolymers produced in the three runs were designated inventioncopolymers 8, 9, and 10, and bad melt flows of 14.3, 6.40 and 10.8respectively. It is believed that lower melt flows are attributable tolower amounts of initiator. The polymerizations of invention runs 8, 9and 10 are shown in Table 10.

TABLE 10 Invention Runs - Second Embodiment Components^(a) Run 8 Run 9Run 10 Step 1 Cyclohexane, phm 145 145 145 Tetrahydrofuran, phm 0.040.04 0.04 n-Butyllithium 0.06 0.05 0.055 initiator, phm Styrene, phm 4040 40 Polymerization Time, min 12 12 12 Peak Polymerization 85 82 84Temperature, ° C. Step 2 n-Butyllitbium 0.06 0.05 0.055 initiator, phmStyrene, phm 10 10 10 Polymerization Time, min 12 12 12 PeakPolymerization 69 69 70 Temperature, ° C. Step 3 Butadiene, phm 12.512.5 12.5 Styrene, phm 12.5 12.5 12.5 Polymerization Time, min 16 16 16Peak Polymerization 84 83 84 Temperature, ° C. Step 4 Butadiene, phm12.5 12.5 12.5 Styrene, phm 12.5 12.5 12.5 Polymerization Time, min 1616 16 Peak Polymerization 96 102 102 Temperature, ° C. Step 5 (Coupling)Vikoflex 7170, phm 0.4 0.4 0.4 Time, min 16 16 16 Temperature, ° C. 8289 89 Step 6 (Terminating) Water, phm 0.2 0.2 0.2 Carbon Dioxide, phm0.4 0.4 0.4 Time, min 25 25 25 Temperature, ° C. 80 82 82 Step 7(Stabilizing) Stabilizer Mixture, phm 1.25 1.25 1.25 Antiblocking agent,phm 0.15 0.15 0.15 Time, min 5 5 5 Temperature, ° C. 80 n.a. 81Recovered Resin Melt Flow, g/10 min 14.3 6.4 10.8 Mw/Mn, thousands154/104 173/115 147/91 Heterogeneity Index 1.48 1.50 1.62 ^(a)After eachaddition of monomer, initiator or additive, the feed lines were rinsedwith approximately 5-20 phm cyclohexane diluent and cleared withnitrogen.

Example IV

Two comparative polymers were used for comparisons of physicalproperties of blends made with polystyrene. Comparative polymer 11 was aresinous styrene-butadiene copolymer with a melt flow of 8.4 g/10 min.Polymer 11 was polymodal from multiple initiator and monomer charges (S,i, i, S. B, i, S, B) and coupled with an epoxidized vegetable oilcoupling agent. Polymer 11 contained nominally 75 wt % styrene and 25 wt% butadiene with no styrene/butadiene tapered blocks. Polymer 11 forms50:50 by weight blends with polystyrene that have high blueness andmodest physical properties.

Comparative polymer 12 was a styrene-butadiene copolymer with no taperedblock segments. Polymer 12 contained nominally 75 wt % styrene and 25 wt% butadiene and had a melt flow of 8.8 g/10 min. It had a polymodalmolecular weight from multiple initiator and monomer charges (S, i, i,S, B) and was coupled with an epoxidized vegetable oil coupling agent.Polymer 12 formed 50:50 blends by weight with polystyrene that have lowblueness and modest impact properties.

Example V

A series of blends of the invention polymers from Examples I and II wasprepared with Novacor® 555 general purpose polystyrene to demonstratethe properties of blends of copolymers containing a single tapered block(invention embodiment 1). Polymer 5 was not included in the blend seriessince it had a melt flow essentially the same as that of polymer 4.Polymers 11 and 12 were also blended with polystyrene for comparison.

The blends were 50:50 by weight and were prepared by solution blendingin cyclohexane in a reactor at 100° C. with stirring for one hour. Eachsolution was flashed to remove the solvent and the polymer was dried,chopped in a granulator, and dried again. The dry polymer was processedon a roll mill and chopped again before injection molding on an Arburgmodel 90 injection molder with zones 1, 2, 3, and nozzle at 210° C.,210° C., 220° C., and 210° C., respectively, to make specimens to testfor properties.

For convenient reference, blends are designated as blends with thecorresponding polymer number and a prime. For example, a blend preparedfrom polymer 1 and polystyrene is blend 1′ and a blend prepared frompolymer 2 and polystyrene is designated blend 2′.

The blend test results are shown in Table 11. Test specimens made fromthe first four blends had less blueness than test specimens made fromthe comparative polymers. Specimens made from blends 6′ and 7′ hadessentially the same blueness as specimens made from blend 12′.

Test specimens made from blends 1′, 2′, 3′, 4′, and 6′ had Izod impactvalues higher than those made from comparative blends 11′ and 12′. Testspecimens made from blend 7′ had a lower Izod impact value than thosemade from the other blends. It is possible that the high level ofinitiator in step two of the polymerization of polymer 7 and theresulting higher melt flow of the final resin prevented improvement inthe Izod impact value of Arburg test specimens made from blends polymer7.

Test specimens made from blends 1′, 2′, and 3′ had higher haze valuesand specimens made from blends 1′ and 2′ had higher melt flows thanthose made from the other blends.

TABLE 11 Physical Properties of Test Specimens Made from Polymer Blendswith Polystyrene^(a) Invention Invention Invention Invention InventionInvention Comparative Comparative Blend Blend Blend Blend Blend BlendBlend Blend Property 1′ 2′ 3′ 4′ 6′ 7′ 11′ 12′ Styrene-butadiene 1 2 3 46 7 11 12 copolymer Blend melt 35.5 30.2 19.0 11.5 10.7 12.8 16.8 17.5flow, g/10 min Haze, % 12.3 8.1 7.1 5.3 3.4 4.2 4.3 2.7 Hunter −15.5−16.2 −15.7 −16.3 −16.9 −17.1 −20.3 −16.8 blueness, b Shore D Hardness76 77 78 77 77 77 77 Notched Izod 14.5 14.6 18.1 20.3 17.1 12.3 12.413.9 impact, J/m Vicat, °83.4 83.4 82.9 86.8 89.8 92.1 92.0 85.3 89.3Tensile strength yield, MPa 39.4 40.2 41.4 43.7 44.5 42.5 37.8 42.6break, MPa 24.8 27.5 29.8 33.6 33.7 21.4 28.0 33.4 Elongation yield, %5.2 5.3 5.3 6.6 6.2 6.2 4.8 4.8 break, % 17.7 18.2 24.9 15.0 14.7 13.732.0 15.77 Flexural 1754 1836 1862 2107 2091 2016 1979 2124 modulus, MPa^(a)50:50 Styrene-butadiene copolymer:polystyrene

Example VI

A series of blends of double tapered block invention polymers (secondinvention embodiment) with polystyrene was prepared to demonstrate theproperties of articles made from the blends. Copolymers 8, 9, and 10from Example III were blended as described in Example V in 50:50 byweight mixtures with general purpose polystyrene to form blends 8′, 9′,and 10′. Test specimens were injection molded from the blends asdescribed in Example V.

The results (Table 12) show that articles made from blends of inventionpolymers 8, 9, and 10 had better Izod impact values than those made fromcomparative blends 11′ and 12′ (shown in Table 11). Articles made fromblends of the invention polymers also have less blueness than those madefrom comparative blend 11′.

TABLE 12 Physical Properties of Polymer Blends With Polystyrene^(a)Invention Invention Invention Comparative Blend Blend Blend BlendProperty 8′ 9′ 10′ 11′ Styrene-butadiene 8 9 10 11 copolymer Blend melt14.8 12.0 14.8 16.8 flow, g/10 min Haze, % 4.1 4.0 5.1 4.3 Hunterblueness, b −17.9 −18.5 −17.9 −20.3 Shore D hardness 76 77 76 77 NotchedIzod 14.9 17.1 19.2 12.3 impact, J/m Vicat softening, ° C. 89.3 90.590.5 85.3 Tensile Strength yield MPa 43.2 43.9 42.5 37.8 break MPa 28.628.7 28.7 28.0 Elongation yield, % 6.4 6.5 6.5 4.8 break, % 17.9 16.713.6 32.0 Flexural 1988 1949 1986 1979 modulus, MPa ^(a)50:50Styrene-butadiene copolymer:polystyrene

Example VII

Three more invention copolymers were prepared on a larger scale todemonstrate further the effect of two butadiene/styrene tapered blocksin improving impact properties of articles made from blends of theinvention copolymers with polystyrene. These polymerizations varied thesize of the two tapered blocks and the weight ratios of initiatorcharges. The polymerizations were carried out in a 380 L reactor.

The polymer polymerization recipes are shown in Table 13. Each polymerwas prepared with the sequence i,S,i,S,B/S,B/S. Polymer 13 had monomercharge weight ratios of 40, 10, 6.9/7.8, 18.1117.2. Polymer 14 hadmonomer charge weight ratios of 40, 10, 5.9/10, 19.1/14.4. Polymer 15had monomer charge ratios of 40, 10, 5.9/10, 19.1/14.4. Monomer chargeratios for polymers 14 and 15 do not add up to 100 phm because of chargeirregularities; actual phm charged is indicated here. The initiatorweight ratios for steps 1:2 in polymerizations 13, 14, find 15 were1:0.79, 1:0.92, and 1:0.89, respectively.

Flow rates for the three polymers wore 7.0, 11.5, and 13.7 g/10 min.

TABLE 13 Invention Runs - Second Embodiment Run 13 Run 14 Run 15 Step 1Cyclohexane, phm 168.9 168.9 168.9 Tetrahydrofuran, phm .04 .04 0.04n-Butyllithium 0.061 0.061 0.065 initiator, phm Styrene, phm 40 40 40Cyclohexane, phm 1.1 1.1 1.1 Peak Polymerization 83 83 83 Temperature, °C. Peak Polymerization 31 32 30 Pressure, psi Step 2 n-Butyllithium0.048 0.056 0.058 initiator, phm Styrene, phm 10 10 10 Cyclohexane, phm1.1 1.1 1.1 Peak Polymerization 81 82 82 Temperature, ° C. PeakPolymerization 35 37 34 Pressure, psi Step 3 Butadiene, phm 6.9 5.9 5.9Styrene, phm 7.8 10 10 Cyclohexane, phm 1.1 1.1 1.1 Peak Polymerization110 109 109 Temperature, ° C. Peak Polymerization 57 58 55 Pressure, psiStep 4 Butadiene, phm 18.1 19.1 19.1 Styrene, phm 17.2 14.4 14.4Cyclohexane, phm 1.1 1.1 1.1 Peak Polymerization 95 98 97 Temperature, °C. Peak Polymerization 52 54 50 Pressure, psi Polymer Analysis (prior tocouping) Mw/Mn, thousands^(a) (GPC area composition)^(b) Peak 1 104/99(64) 100/95 (63) 95/90 (64) Peak 2  50/46 (36)  47/44 (37) 46/43 (36)Step 5 (Coupling) Vikoflex 7170, phm 0.4 0.4 0.4 Cyclohexane, phm 0.550.55 0.55 Temperature, ° C. 88 86 88 Pressure, psi 50 52 48 Step 6(Terminating) Water, phm 13 13 13 Carbon Dioxide, phm 0.1 0.1 0.1Temperature, ° C. 87 87 87 Pressure, psi 50 50 50 Step 7 (Stabilizing)Stabilizer Mixture, phm 1.25 1.25 1.25 Antiblocking agent, phm 0.3 0.30.3 Recovered Resin Melt Flow, g/10 min 7.0 11.5 13.7 ^(a)Polystyreneequivalent Mw/Mm. Mw/Mn of polystyrene with the same hydrodynamic volumeas the polymer peak. ^(b)Response of a dielectric detector in an AppliedAutomation process control GPC.

Example VIII

Two comparative polymers (16 and 17) were prepared for comparison withthe invention polymers from Example VII. Polymer 16 was a coupledpolymodal styrene/butadiene copolymer containing 75 wt % styrene and 25wt % butadiene. Polymer 16 was prepared with the sequencei,S,i,S,B/S,i,S,B using monomer charge weight ratios of 37, 19, 7.5/5,14, 17.5, respectively.

Polymer 17 was a coupled polymodal styrene/butadiene copolymercontaining 70 wt % styrene and 30 wt % butadiene. Polymer 17 was;prepared with the sequence i,S,i,S,B,i,S,B using monomer charge weightratios of 37, 19, 9, 14, 21, respectively.

These comparative polymers were prepared in a 380 L reactor according tothe procedure in Table 14.

Polymer 16 yielded blends with polystyrene which were made into testspecimens that had low blueness and modest physical properties. Polymer17 formed blends with polystyrene which were made into test specimensthat had high blueness and good physical properties.

The flow rates for polymers 16 and 17 were 8.2 and 8.6 g/10 min,respectively.

TABLE 14 Invention Runs - Second Embodiment Components^(a) Run 16 Run 17Step 1 Cyclohexane, phm 168 168 Tetrahydrofuran, phm 0.02 0.02n-Butyllithium 0.034 0.031 initiator, phm Styrene, phm 37 37 PeakPolymerization Temperature, ° C. 88 87 Peak Polymerization Pressure, psi37 36 Step 2 n-Butyllithium 0.048 0.053 initiator, phm Styrene, phm 1919 Peak Polymerization 86 85 Temperature, ° C. Peak PolymerizationPressure, psi 33 32 Step 3 Butadiene, phm 7.5 9 Styrene, phm 5 0 PeakPolymerization 82 83 Temperature, ° C. Peak Polymerization Pressure, psi37 36 Step 4 n-Butyllithium initiator, phm 0.085 0.110 Styrene, phm 1414 Peak Polymerization 87 85 Temperature, ° C. Peak PolymerizationPressure, psi 41 40 Step 5 Butadiene 17.5 21 Peak PolymerizationTemperature, ° C. 101 107 Peak Polymerization Pressure, ° C. 54 58 Step6 (Coupling) Vikoflex 7170, phm 0.4 0.4 Temperature, ° C. 89 95Pressure, psi 51 54 Step 7 (Terminating) Water, phm 13 13 CarbonDioxide, phm 0.1 0.1 Temperature, ° C. 87 87 Pressure, psi 50 50 Step 8(Stabilizing) Stabilizer Mixture, phm 1.25 1.25 Antiblocking agent, phm0.3 0.3 Recovered Resin Melt Flow, g/10 min 8.2 8.6 ^(a)After eachaddition of monomer, initiator or additive, the feed lines were rinsedwith approximately 5-20 phm cyclohexane diluent and cleared withnitrogen.

Example IX

Polymers from Examples VII and VIII were blended with Novacor® 555general purpose polystyrene to produce blends 13′, 14′, 15′, 16′, and17′ for evaluation. The resulting blend was extruded on an 8.9 cmdiameter extruder and sheet line. All blends were 50:50 by weight exceptfor blend 16′, which was a 60:40 copolymer:polystyrene by weight blend.A 0.51 mm die gap opening was used for the preparation of a 0.38 mmthick extruded sheet for evaluation.

The extruded sheet samples were evaluated and the results are shown inTable 15. The fold test involves bending the sheet on itself in themachine direction (MD) to induce a transverse directional (TD) break.The sheet is folded at two different rates to allow differentiationbetween brittle sheet samples. In addition, the behavior of the sheet inresponse to a tear in machine and transverse directions was determined.

Sheets made from invention blends 13′, 14′ and 15′ all had less bluenessthan sheets made from comparative blend 17′, but more blueness thansheets made from comparative blend 16′.

Sheets made from blend 13′ had the highest total energy dart drop valueof sheets from this set of blends. Sheets made from blends 14′ and 15′had low total energy dart drop values similar to the values of sheetsmade from blend 16′. Sheets made from comparative blend 16′ had thelowest blueness value of any in the group, but had a low total energydart drop value and brittle fold test. Sheets made from comparativeblend 17′ bad the highest blueness value and better ductility thaninvention blends 14′ and 15′.

TABLE 15 Physical Properties of Polymer Blends With Polystyrene Compar-Compar- Invention Invention Invention ative ative Blend Blend BlendBlend Blend Property 13′ 14′ 15′ 16′ 17′ Styrene- 13 14 15 16 17butadiene copolymer Copolymer: 50:50 50:50 50:50 60:40 50:50 Styreneblend ratio Hunter −8.0 −10.0 −10.1 −5.7 −13.5 blueness b Haze, % 2.462.48 2.97 1.63 3.60 Trans- 89.6 89.3 89.2 89.8 88.8 mission, % Totalenergy 3.17 0.80 1.11 0.95 1.61 dart drop, J Transverse D/D B/D B/D B/BD/D direction Fold^(a) (fast/slow) Machine D D D D D direction Tear^(a)Transverse D D D D D direction Tear^(a) ^(a)D = ductile, B = brittle.

These results show that either of the embodiments of the invention canbe used in blends with polymers of styrene to produce resins from whichcan be made articles having low blueness and other properties comparableto or better than the properties of articles Lade from blends ofpolymers of styrene with other monovinylaromatic/conjugated dienecopolymers. More particularly, a comparison of the 50:50(copolymer:styrene) invention blends 13′, 14′ and 15′ with the 60:40(copolymer:styrene) comparative blend 16′ shows that a smaller amount ofinvention copolymer than comparative copolymer can be used to showcomparable improvements in reduction of blueness,. Other surprisingblend properties are demonstrated by these runs. For example, inventionblend 13′ which had a total of about 75 wt % total styrene in the blendcomposition had total energy dart drop of 3.17 J compared to a totalenergy dart drop of 1.61 J for comparative blend 17′ which had onlyabout 70 wt % total styrene in the blend composition.

While the polymers and methods of this invention have been described indetail for the purpose of illustration, the inventive polymers andmethods are not to be construed as limited thereby. This patent isintended to cover all changes and modifications within the spirit andscope thereof.

That which is claimed is:
 1. A composition of matter comprising apolymer of styrene, and a polymodal composition wherein said polymodalcomposition comprises coupled tapered block copolymers, wherein saidcoupled tapered block copolymers consist of S-S-B/S-B/S-x-S/B-S/B-S-S,S-B/S-B/S-x-S/B-S/B-S, and S-S-B/S-B/S-x-S/B-S/B-S copolymers, andwherein S=monovinylaromatic block B=conjugated diene block B/S=taperedblock of conjugated diene/monovinylaromatic compound, and x=couplingagent and wherein said composition of matter substantially contains onlycoupled tapered block copolymer from said polymodal composition.
 2. Acomposition of matter as recited in claim 1 wherein said polymer ofstyrene is present in an amount in the range from 10 weight percent to70 weight percent, based on the total weight of said composition ofmatter.
 3. Articles made from said composition of matter of claim
 1. 4.Articles made from said composition of matter of claim
 2. 5. Acomposition of matter as recited in claim 2 wherein said polymer ofstyrene is present in an amount in the range from about 20 weightpercent to about 65 weight percent, based on total weight of saidcomposition of matter.
 6. Articles made from said composition of matterof claim
 5. 7. Articles made from said composition of matter of claim 8.8. A composition of matter as recited in claim 5 wherein said polymer ofstyrene is present in an amount in the range from about 30 weightpercent to about 60 weight percent, based on total weight of saidcomposition of matter.
 9. A composition of matter according to claim 8wherein said S consists essentially of styrene and said B consistsessentially of butadiene.
 10. A composition of matter comprising apolymer of styrene, and a polymodal composition wherein said polymodalcomposition comprises coupled block copolymers, where said coupledtapered block copolymers consist of S-S-B/S-B/S-x-S/B-S/B-S-S,S-B/S-B/S-x-S/B-S/B-S, and S-S-B/S-B/S-x-S/B-S/B-S copolymers, andwherein S=monovinylaromatic block B=conjugated diene block B/S=taperedblock of conjugated diene/monovinylaromatic compound, and x=couplingagent and wherein said composition of matter substantially contains onlycoupled tapered block copolymers from said polymodal composition andwherein said polymodal composition is produced by the process comprising(a) charging a monovinylaromatic monomer and an initiator, and in thepresence of a randomizer, allowing polymerizing to occur untilessentially no free monomer is present, to produce a S-Li block;thereafter (b) charging an initiator and a monovinylaromatic monomer,and allowing polymerization to occur until essentially no free monomeris present, to produce S-S-Li and S-Li blocks; thereafter (c) charging amixture of monovinylaromatic monomer and conjugated diene monomer, andallowing polymerization to occur until essentially no free monomer ispresent, to produce S-S-B/S-Li and S-B/S-Li blocks; thereafter (d)charging a mixture of monovinylaromatic monomer and conjugated dienemonomer, and allowing polymerization to occur until essentially no freemonomer is present, to produce S-S-B/S-B/S-Li and S-B/S-B/S-Li blocks;and thereafter (e) charging the reaction mixture with a coupling agentto form said coupled tapered block copolymers.
 11. A composition ofmatter as recited in claim 10 wherein said polymer of styrene is presentin an amount in the range from 10 weight percent to 70 weight percent,based on the total weight of said composition of matter.
 12. Acomposition of matter as recited in claim 11 wherein said polymer ofstyrene is present in an amount in the range from about 20 weightpercent to about 65 weight percent, based on total weight of saidcomposition of matter.
 13. A composition of matter as recited in claim12 wherein said polymer of styrene is present in an amount in the rangefrom about 30 weight percent to about 60 weight percent, based on totalweight of said composition of matter.
 14. Articles made from saidcomposition of matter of claim
 10. 15. Articles made from saidcomposition of matter of claim
 9. 16. Articles made from saidcomposition of matter of claim
 11. 17. Articles made from saidcomposition of matter of claim
 12. 18. Articles made from saidcomposition of matter of claim
 13. 19. A composition of matter accordingto claim 13 wherein said S consists essentially of styrene and said Bconsists essentially of butadiene.
 20. Articles made from saidcomposition of matter of claim 19.